1. Field of the Invention
The present invention relates to Generic Access Network (GAN), and more particularly to a method for establishing a connection with a generic access network and an associated GAN-enabled mobile station.
2. Description of the Prior Art
Generic Access Network (GAN), also known as Unlicensed Mobile Access (UMA), is a mobile communication standard developed by the 3rd Generation Partnership Project (3GPP) that extends mobile services (voice or data) over IP access networks. In a generic access network, a GAN-enabled mobile station or user equipment can get mobile services by establishing an IP connection with a GAN controller (GANC), which connects to a mobile core network. The GAN-enabled mobile station establishes the IP connection with the GANC via wireless IP technology, e.g. Wi-Fi, Bluetooth, etc. The most common application of GAN is in a dual-mode handset service where subscribers can seamlessly roam and handover between wireless LANs and 2G/3G mobile networks by using a GAN-enabled mobile station, e.g. a GSM/Wi-Fi dual-mode mobile phone. Some mobile operators, such as Orange, T-Mobile, etc. have already begun to provide GAN/UMA service to their subscribers.
In current specification of 3GPP TS 44.318, it is defined how the GAN-enabled mobile station establishes a connection with the generic access network. FIG. 1 and FIG. 2 are diagrams respectively showing a successful case and a failure case of initiation of a Generic Access-Circuit Switched Resources (GA-CSR) connection. As shown, when a mobile station (denoted as MS) in GA-CSR-IDLE state initiates a GA-CSR connection via a GA-CSR REQUEST message to the GANC, the MS will also start the TU3908 timer with a default timeout of 5 seconds. If the MS receives a GA-CSR REQUEST ACCEPT message from the GANC within the timeout of the TU3908 timer, then the MS will stop the TU3908 timer and move into GA-CSR-DEDICATED state, as shown in FIG. 1; if the MS receives a GA-CSR REQUEST REJECT message from the GANC within the timeout of TU3908, then the MS will stop the TU3908 timer and remain in GA-CSR-IDLE state, as shown in FIG. 2.
However, if the MS does not receive any response from the GANC within the timeout of TU3908, which may result from that the GANC does not respond in time or even never respond to the MS (maybe due to weak RF signal or network traffic jam), then the MS just stays in GA-CSR-IDLE state according to 3GPP TS 44.318 section 7.1.4.1. The MS may retry to establish the connection several times, but the same no-response result can still occur because of the critical network environment. This incurs uncomfortable user experience.
Similarly, the same problem happens in packet-switched service side. FIG. 3 is a diagram showing the initiation of a Generic Access-Packet Switched Resources (GA-PSR) connection. As shown, when the MS in GA-PSR-STANBY state initiates a GA-PSR connection via a GA-PSR ACTIVATE UTC REQ message to the GANC, the MS will also start the TU4002 timer with a default timeout of 5 seconds. If the MS receives a GA-PSR ACTIVATE UTC ACK message from the GANC within the timeout of the TU4002 timer, the MS will stop the TU4002 timer, start the TU4001 timer, and move into GA-PSR-ACTIVE state, as shown in FIG. 3. However, if the MS does not receive any response from the GANC within the timeout of TU4002, then the MS has the chance to stick in the idle state and cannot initiate any packet-switched service.